Laser levelling and setting apparatus as well as other optical based apparatus such as automatic levels and theodolites are typically used in the surveying, building and construction industries to measure angles and inclination, for marking out, or to align walls and ceilings, for example.
Laser levelling apparatus in particular are used to generate reference lines, for example, by sweeping a laser beam in a plane and either observing a reflection line on a surface, or alternatively using electronic detectors to detect the beam. Known devices typically project a vertical laser beam into a 45° rotating prism which then reflects a horizontal sweeping beam. With these devices the beam is generally only rotated in a single plane, which is normally horizontal. With some devices it is possible to change from a horizontal to a vertical plane however this usually requires disassembling the laser head from the body and reassemble in an alternative configuration.
Still other devices allow for tilting of the laser to thereby create an angled beam for applications such as defining slopes and the like. However the tilt angle of such devices is normally restricted because the positioning of the laser head on the body results in the periphery of the body blocking the laser at certain angles. Thus these apparatus suffer from the drawback of lack of range of movement of the laser beam and are therefore restricted to use in relatively simple marking out tasks.
Some other known apparatus do allow the laser beam to be projected down through the centre of the apparatus so that the apparatus can be used to give a plumb line and to accurately align the apparatus over a style marking a specific reference point on a work site. Subsequently, apparatus have been developed which have two or three axes of rotation of a laser head but do not allow the laser to be projected down the centre of the apparatus. These apparatus do however provide an increase in the degree of movement but with that increase in movement comes problems with accuracy of movement of the laser. In U.S. Pat. No. 4,988,192 to Knittel, a laser levelling apparatus of the above type is disclosed. In that apparatus a laser diode is housed in a laser head which is in turn supported on a body. The laser head contains a laser as well as a prism for reflecting the laser beam at 90 degrees. The body is rotatable about a vertical axis and the laser head is in turn rotatable about a horizontal axis. The laser head itself is also rotatable about a third axis which is transverse to the direction of the laser beam projected from the head. Rather than rotating a prism to sweep the laser beam, the laser head is rotated. In this case the laser head contains a optical quality prism and a laser source and therefore the weight contained in the laser head exerts a significant load on the drive means used to rotate the head to sweep the laser. In addition the uneven distribution of weight may result in stability problems with the apparatus.
A further problem with many of the known apparatus is that a single instrument cannot be used to perform all of the end functions required by the end user, and in those instruments that do allow more than one function, it is usually necessary to ‘set up’ the instrument between different functions.